Apparatus and method for cleaning solder paste from items associated with surface mount technology manufacturing

Abstract

An apparatus and method for cleaning solder paste from stencils, screens, misprinted circuit boards, and tools associated with the manufacturing of surface mount technology circuit boards. The apparatus includes a holder assembly for holding the solder-laden objects during cleaning and rotatable spray arms connected with a chemical pump for spraying a transversely directed, cyclic waves of solvent onto the object's surfaces. The cleaning action of the spray arms permits use of the solvent at or below room temperature thereby substantially reducing evaporative loss of solvent, environmental injury resulting from such evaporative loss, and exposure of workers to solvent vapors. The apparatus includes filters for filtering heavy metal particles washed from the objects to contain the heavy metals for safe disposal. Safety mechanisms are included in the apparatus to prevent worker injury. The apparatus includes a timer/control unit which automatically controls the sequence and duration of the apparatus' components during a cleaning cycle. The method includes cleaning of solder paste by cyclically exposing the object surfaces to jets of solvent at directions constantly transverse to the surfaces thereby creating wavefronts of solvent which mechanically wipe solder paste from the surfaces.

We claim: 
     
       1. An apparatus for cleaning solder paste from a first surface of a substantially planar object comprising: a first rotatable spray arm being situated within a cleaning chamber and rotatably supported on a first cleaning chamber wall of said cleaning chamber, said first spray arm having a plurality of nozzles along its length fixedly oriented for directing a liquid through said nozzles perpendicularly to said length of said first spray arm and transversely to a first plane of rotation of said first spray arm in a direction intersecting a second cleaning chamber wall opposite said first cleaning chamber wall, said cleaning chamber having a cleaning chamber external opening through which said planar object may be inserted and removed from said cleaning chamber and a cleaning chamber drain port through which said liquid may drain from said cleaning chamber;   a sump tank in fluid communication with said cleaning chamber drain port by means of a pipe sealingly attached to said drain port and extending into said sump tank for receiving all of said liquid which drains from said cleaning chamber;   a stencil/frame holder assembly for holding said planar object in said cleaning chamber so a surface of said planar object is oriented substantially parallel with said first plane of rotation and positioned whereby said liquid from said nozzles strikes said surface, said stencil/frame holder assembly being sized for carrying said planar object through said cleaning chamber's external opening for placing said planar object in said cleaning chamber or removing said planar object therefrom, said stencil/frame holder is a frame-like assembly comprising two vertically oriented side members rigidly joined to form a rectangular structure with a horizontally oriented stencil/frame holder top and a horizontally oriented stencil/frame support member, and further comprising a horizontally oriented retainer rail slidably engaged with said side members, said retainer rail and said stencil/frame support member each having a channel facing inward of said rectangular structure for securing said planar object for cleaning by said apparatus, said stencil/frame holder top and said stencil frame support member being slidably coupled with tracks joined with and supported by a gantry framework in turn mounted on and supported by said apparatus casing, said tracks extending from said cleaning chamber external opening to an area outside of said cleaning chamber along said gantry framework sufficient for slidably carrying said planar object held by said stencil/frame holder fully into and from said cleaning chamber;   chamber sealing means for substantially sealing said cleaning chamber external opening with said stencil/frame holder assembly within said cleaning chamber;   a pump having an input port and an output port for propelling said liquid introduced into said input port at a low pressure frame said output port at an elevated pressure;   a first conduit assembly in sealed fluid communication with a sump tank exit port and with said pump's input port for drawing said liquid from said sump tank to said input port;   a second conduit assembly in sealed fluid communication with said pump's output port and with said first rotatable spray arm for conducting said liquid from said pump to said first spray arm;   an apparatus casing sized and shaped for substantially enclosing within its bounds said cleaning chamber, said sump tank, said pump, said first conduit assembly, and said second conduit assembly, said apparatus casing having a first aperture through which the portion of said cleaning chamber having said cleaning chamber external opening extends, said cleaning chamber and said apparatus casing being sealingly joined one to the other at said aperture, said apparatus casing further comprising a hinged access door overlying a second aperture for allowing access to said sump tank, said pump, said first conduit assembly, and said second conduit assembly for maintaining said apparatus.   
     
     
       2. The invention of claim 1 wherein said chamber sealing means is incorporated into said stencil/frame holder top by shaping said stencil/frame holder top for matingly coupling with said cleaning chamber at said cleaning chamber's external opening when said stencil/frame holder assembly is fully positioned within said cleaning chamber. 
     
     
       3. The invention of claim 2 further comprising a stencil/frame holder assembly hoist mechanism engaged with said stencil/frame holder assembly for moving said stencil/frame holder assembly along said tracks into and from said cleaning chamber. 
     
     
       4. The invention of claim 3 wherein said stencil/frame holder assembly hoist mechanism comprises a bi-directional electric motor mounted on a gantry framework cross member, a pinion keyed to said motor's armature shaft, a rack slidably mounted on said gantry framework cross member and engaged with said pinion, a chain coupled at a first chain end with an end of said rack and at a second chain end with said stencil/frame holder top, and a switch for actuating said motor alternatively in its two directions for alternatively moving said stencil/frame holder assembly along said tracks into and from said cleaning chamber under power of said motor. 
     
     
       5. The invention of claim 4 further comprising an electromagnetic brake mechanism mounted on said gantry framework cross member and associated with said armature shaft of said electric motor, said brake mechanism including a braking mechanism solenoid with a braking element mounted on a braking mechanism solenoid piston of said braking mechanism solenoid, said piston being spring-biased whereby said braking element is held against said armature shaft, said braking mechanism solenoid being connected with a power source whereby when power is applied to said braking mechanism solenoid, said piston is retracted within said braking mechanism solenoid against resistance of said spring thereby disengaging said braking element from said armature shaft, said braking mechanism for preventing movement of said stencil/frame holder assembly along said tracks unless power is directed to said braking mechanism solenoid. 
     
     
       6. The invention of claim 5 further comprising a safety stop mechanism for preventing accidental movement of said stencil/frame holder assembly toward said cleaning chamber, said safety stop mechanism comprising a safety stop solenoid and a safety stop solenoid piston, said safety stop solenoid piston having its external end fashioned into a ratchet lever permitting hinged movement of said external end through approximately forty-five degrees in a single plane, said safety stop solenoid and piston being constructed, mounted on an upright gantry framework member, and positioned relative to said track on said upright gantry framework member whereby said external end may be moved between an extended position where passage of said stencil/frame holder top toward said cleaning chamber opening is blocked by said external end and a retracted position where said stencil/frame holder top may pass said safety stop mechanism toward said cleaning chamber opening, said safety stop solenoid piston being spring biased toward said extended position, said safety stop solenoid being connected with a source of intermittent power whereby, when power is applied to said safety stop solenoid, said safety stop solenoid piston is retracted to permit said stencil/frame top to be directed toward said cleaning chamber opening for a cleaning cycle of said apparatus. 
     
     
       7. The invention of claim 6 wherein an end of said pipe which connects said cleaning chamber drain port with said sump tank extends into the interior of said sump tank and has an external annular flange at said end for permitting a filter bag to be attached at said end of said pipe for filtering particulate from said liquid as said liquid flows from said cleaning chamber. 
     
     
       8. The invention of claim 7 further comprising a cartridge filter assembly incorporated into said second conduit assembly for diverting said liquid from said second conduit assembly, filtering particulates from said liquid, and reintroducing said liquid into said second conduit assembly prior to said liquid's reaching said rotatable spray arm. 
     
     
       9. The invention of claim 8 wherein said cartridge filter assembly includes a filter cartridge capable of filtering particulates as small as five microns in diameter. 
     
     
       10. The invention of claim 8 further comprising a timer/control unit which, through selectively self-actuated internal switches respectively controlling current flow to said bi-directional motor, to said pump, to said brake mechanism solenoid, and to said safety stop solenoid, actuates said electric motor, said pump, said brake mechanism solenoid, and said safety stop solenoid in a prescribed temporal arrangement for sequentially disengaging said brake mechanism, retracting said external end of said safety stop solenoid piston, actuating said electric motor in the direction for moving said stencil/frame holder assembly from a starting position into said cleaning chamber and thereby sealing said cleaning chamber's external opening, reengaging said braking mechanism after said stencil/frame holder top is seated at said cleaning chamber opening, re-extending said safety stop solenoid piston, actuating said pump for a prescribed period of time, following a duration of time after operation of said pump disengaging said brake mechanism, actuating said electric motor in the direction for moving said stencil/frame holder assembly from said cleaning chamber, and reengaging said braking mechanism after said stencil/frame holder assembly returns to said starting position, said timer/control unit further comprising sensing device receiving means for receiving a signal from an external sensing device and interrupting power to said bi-directional motor, said pump, said brake mechanism solenoid, and said safety stop solenoid when said signal is received. 
     
     
       11. The invention of claim 10 further comprising a second rotatable spray arm substantially identical to said first rotatable spray arm, said second spray arm being rotatably supported on said second cleaning chamber wall, said second spray arm having a plurality of nozzles along its length fixedly-oriented for directing a liquid through said nozzles perpendicularly to said length of said second spray arm and transversely to a second plane of rotation of said second spray arm in a direction intersecting said first plane of rotation of said first spray arm, said second spray arm being in fluid communication with said second conduit assembly and thereby conducting said liquid from said pump through said second spray arm's nozzles for cleaning a second side of said planar object opposite said first side. 
     
     
       12. The invention of claim 11 wherein said first and second rotatable spray arms each comprise two spray arm tubes coupled at interior ends and in fluid communication with an internal chamber of a rotatably mounted hub, said hubs in turn being in fluid communication with said second conduit assembly, said spray arm tubes external ends being occluded, said spray arm tubes having said nozzles situated along their lengths, said two spray arm tubes of each said spray arms being respectively oriented whereby said liquid flowing from said nozzles imparts rotation to said spray arms and whereby said liquid from said first and second spray arms transversely impinges said first and second planar object surfaces respectively, said rotation and nozzle orientation of said spray arms creating waves of said liquid to pass over said planar object surfaces for wiping material from said planar object surfaces. 
     
     
       13. The invention of claim 12 further comprising refrigeration cooling coils extending from outside of said apparatus casing into said cleaning chamber and said sump tank, said cooling coils having fittings formed at cooling coil ends situated outside of said apparatus casing permitting connection of said cooling coils with refrigeration components whereby said cooling coils may act to cool said liquid within said cleaning chamber and said sump tank for reducing temperature at which said liquid is used within said apparatus. 
     
     
       14. The invention of claim 13 further comprising distillation means for distilling said liquid having been used in said apparatus and being saturated with contaminants washed from said planar object surfaces. 
     
     
       15. The invention of claim 14 wherein said distillation means comprises a distillation tank with heating means incorporated therein, a recovery tank for receiving condensed, distilled said liquid, and cooling coils in sealed fluid communication with said the respective interiors of said distillations tank and said recover tank, said distillation means being incorporated into said second conduit by means of a bi-directional valve whereby said liquid from said pump may be diverted from said second conduit assembly into a still pipe which is in fluid communication with said distillation tank thereby removing said liquid from said sump tank to said distillation means for distillation. 
     
     
       16. The invention of claim 15 further comprising a light curtain system, said light curtain system comprising an optical transceiver and a plurality of mirrors oriented whereby vertical planes of light are projected from said optical transceiver around said apparatus' perimeter to encompass said apparatus and are received by said transceiver, said transceiver having light plane interruption detecting means for detecting a breach of said light plane and further having means for sending an electrical signal to said sensing device receiving means of said timer/control unit, said light curtain system in conjunction with said sensing device receiving means for interrupting operation of said apparatus when a user extends a bodily member within the perimeter defined by said light planes to prevent bodily injury. 
     
     
       17. The invention of claim 16 wherein said pump is designed for and capable of propelling liquid at a rate of 40 gallons per minute at a pressure of 80 water feet through said output port. 
     
     
       18. An apparatus for cleaning solder paste from a first surface of a substantially planar object used in surface-mount-technology manufacturing processes comprising: a first rotatable spray arm being situated within a cleaning chamber and rotatably supported on a first cleaning chamber wall of said cleaning chamber, said first spray arm having a plurality of nozzles along its length fixedly oriented for directing a liquid through said nozzles perpendicularly to said length of said first spray arm and transversely to a first plane of rotation of said first spray arm in a direction intersecting a second cleaning chamber wall opposite said first cleaning chamber wall, said cleaning chamber having a cleaning chamber external opening through which said planar object may be inserted and removed from said cleaning chamber and a cleaning chamber drain port through which said liquid may drain from said cleaning chamber;   a second rotatable spray arm substantially identical to said first rotatable spray arm, said second spray arm being rotatably supported on said second cleaning chamber wall, said second spray arm having a plurality of nozzles along its length fixedly oriented for directing a liquid through said nozzles perpendicularly to said length of said second spray arm and transversely to a second plane of rotation of said second spray arm in a direction intersecting said first plane of rotation of said first spray arm, said second spray arm being in fluid communication with said second conduit assembly and thereby conducting said liquid from said pump through said second spray arm's nozzles for cleaning a second side of said planar object opposite said first side;   a sump tank in fluid communication with said cleaning chamber drain port by means of a pipe sealingly welded to said drain port and extending into said sump tank for receiving all of said liquid which drains from said cleaning chamber, an end of said pipe extending into the interior of said sump tank and having an external annular flange at said end for permitting a filter bag to be attached at said end of said pipe for filtering particulate from said liquid as said liquid flows from said cleaning chamber;   a stencil/frame holder assembly for holding said planar object in said cleaning chamber so a surface of said planar object is oriented substantially parallel with said first plane of rotation and positioned whereby said liquid from said nozzles strikes said surface, said stencil/frame holder assembly being sized for carrying said planar object through said cleaning chamber external opening for placing said planar object in said cleaning chamber or removing said planar object therefrom, said stencil/frame holder being a frame-like assembly comprising two vertically oriented side members rigidly joined to form a rectangular structure with a horizontally oriented stencil/frame holder top and a horizontally oriented stencil/frame support member, and further comprising a horizontally oriented retainer rail slidably engaged with said side members, said retainer rail and said stencil/frame support member each having a channel facing inward of said rectangular structure for securing said planar object for cleaning by said apparatus, said stencil/frame holder top and said stencil frame support member being slidably coupled with tracks joined with and supported by a gantry framework in turn mounted on and supported by said apparatus casing, said tracks extending from said cleaning chamber external opening to an area outside of said cleaning chamber along said gantry framework sufficiently for slidably carrying said planar object held by said stencil/frame holder fully into and from said cleaning chamber;   a pump having an input port and an output port for propelling said liquid introduced into said input port at a low pressure from said output port at an elevated pressure;   a first conduit assembly in sealed fluid communication with a sump tank exit port and with said pump's input port for drawing said liquid from said sump tank to said input port;   a second conduit assembly in sealed fluid communication with said pump's output port and with said first and second rotatable spray arms for conducting said liquid from said pump to said spray arms;   an apparatus casing sized and shaped for substantially enclosing within its bounds said cleaning chamber, said sump tank, said pump, said first conduit assembly, and said second conduit assembly, said apparatus casing having a first aperture through which said cleaning chamber's face having said cleaning chamber external opening extends, said cleaning chamber and said apparatus casing being sealingly joined one to the other at said aperture, said apparatus casing further comprising a hinged access door overlying a second aperture for allowing access to said sump tank, said pump, said first conduit assembly, and said second conduit assembly for maintaining said apparatus;   chamber sealing means incorporated into said stencil/frame holder top by shaping said stencil/frame holder top for matingly coupling with said cleaning chamber at said cleaning chamber external opening when said stencil/frame holder assembly is maximally positioned within said cleaning chamber;   a stencil/frame holder assembly hoist mechanism engaged with said stencil/frame holder assembly for moving said stencil/frame holder assembly along said tracks into and from said cleaning chamber, said stencil/frame holder assembly hoist mechanism comprising a bi-directional electric motor mounted on a gantry framework cross member, a pinion keyed to said motor's armature shaft, a rack slidably mounted on said gantry framework cross member and engaged with said pinion, a chain coupled at a first chain end with an end of said rack and at a second chain end with said stencil/frame holder top, and a switch for actuating said motor alternatively in its two directions for alternatively moving said stencil/frame holder assembly along said tracks into and from said cleaning chamber under power of said motor;   an electromagnetic brake mechanism mounted on said gantry framework cross member and associated with said armature shaft of said electric motor, said brake mechanism including a braking mechanism solenoid with a braking element mounted on a braking mechanism solenoid piston of said braking mechanism solenoid, said piston being spring-biased whereby said braking element is held against said armature shaft, said braking mechanism solenoid being connected with a power source whereby when power is applied to said braking mechanism solenoid, said piston is retracted within said braking mechanism solenoid against resistance of said spring thereby disengaging said braking element from said armature shaft, said braking mechanism for preventing movement of said stencil/frame assembly along said tracks unless power is directed to said braking mechanism solenoid;   a safety stop mechanism for preventing accidental movement of said stencil/frame holder assembly toward said cleaning chamber, said safety stop mechanism comprising a safety stop solenoid and a safety stop solenoid piston, said safety stop solenoid piston having its external end fashioned into a ratchet lever permitting hinged movement of said external end through approximately forty five degrees in a single plane, said safety stop solenoid and piston being constructed, mounted on an upright gantry framework member, and positioned relative to said track on said upright gantry framework member whereby said external end may be moved between an extended position where passage of said stencil/frame holder top toward said cleaning chamber opening is blocked by said external end and a retracted position where said stencil/frame holder top may pass said safety stop mechanism toward said cleaning chamber opening, said safety stop solenoid piston being spring biased toward said extended position, said safety stop solenoid being connected with a source of intermittent power whereby, when power is applied to said safety stop solenoid, said safety stop solenoid piston is retracted to permit said stencil/frame top to be directed toward said cleaning chamber opening for a cleaning cycle of said apparatus;   a cartridge filter assembly incorporated into said second conduit assembly for diverting said liquid from said second conduit assembly, filtering particulates from said liquid, and reintroducing said liquid into said second conduit assembly prior to said liquid's reaching said first and second spray arms;   a timer/control unit which, through selectively self-actuated internal switches respectively controlling current flow to said bi-directional motor, to said pump, to said brake mechanism solenoid, and to said safety stop solenoid, actuates said electric motor, said pump, said brake mechanism solenoid, and said safety stop solenoid in a prescribed temporal arrangement for sequentially disengaging said brake mechanism, retracting said external end of said safety stop solenoid piston, actuating said electric motor in the direction for moving said stencil/frame holder assembly from a starting position into said cleaning chamber and thereby sealing said cleaning chamber's external opening, reengaging said braking mechanism after said stencil/frame holder top is seated at said cleaning chamber opening, re-extending said safety stop solenoid piston, actuating said pump for a prescribed period of time, disengaging said brake mechanism following a duration of time after operation of said pump; actuating said electric motor in the direction for moving said stencil/frame holder assembly from said cleaning chamber, and reengaging said braking mechanism after said stencil/frame holder assembly returns to said starting position, said timer/control unit further comprising sensing device receiving means for receiving a signal from an external sensing device and interrupting power to said bi-directional motor, said pump, said brake mechanism solenoid, and said safety stop solenoid when said signal is received;   refrigeration cooling coils extending from outside of said apparatus casing into said cleaning chamber and said sump tank, said cooling coils having fittings formed at cooling coil ends situated outside of said apparatus casing permitting connection of said cooling coils with refrigeration components whereby said cooling coils may act to cool said liquid within said cleaning chamber and said sump tank for reducing temperature at which said liquid is used within said apparatus; and   distillation means for distilling said liquid having been used in said apparatus and being saturated with contaminants washed from said stencil/frame combination surfaces, said distilling means comprising a distillation tank with heating means incorporated therein, a recovery tank for receiving condensed, distilled said liquid, and cooling coils in sealed fluid communication with said respective interiors of said distillations tank and said recover tank, said distillation means being incorporated into said second conduit by means of a bi-directional valve whereby said liquid from said pump may be diverted from said second conduit assembly into a still pipe which is in fluid communication with said distillation tank thereby removing said liquid from said sump tank to said distillation means for distillation.   
     
     
       19. The invention of claim 18 wherein said first and second rotatable spray arms each comprise two spray arm tubes coupled at interior ends and in fluid communication with an internal chamber of a rotatably mounted hub, said hubs in turn being in fluid communication with said second conduit assembly, said spray arm tubes external ends being occluded, said spray arm tubes having said nozzles situated along their lengths, said two spray arm tubes of each said spray arms being respectively oriented whereby said liquid flowing from said nozzles imparts rotation to said spray arms and whereby said liquid from said first and second spray arms transversely impinges said first and second planar object surfaces respectively, said rotation and nozzle orientation of said spray arms creating waves of said liquid to pass over said planar object surfaces for wiping material from said planar object surfaces. 
     
     
       20. The invention of claim 19 further comprising a light curtain system, said light curtain system comprising an optical transceiver and a plurality of mirrors oriented whereby vertical planes of light are projected from said optical transceiver around said apparatus, perimeter to encompass said apparatus and are received by said transceiver, said transceiver having light plane interruption detecting means for detecting a breach of said light plane and further having means for sending an electrical signal to said sensing device receiving means of said timer/control unit, said light curtain system in conjunction with said sensing device receiving means for interrupting operation of said apparatus when a user extends a bodily member within the perimeter defined by said light planes to prevent bodily injury.